The problem arose when i came to wire it, all the sites on the internet giving the wiring for a Subaru Legacy 1999 did not match what I had. Eventually I found the socket wiring for a Clarion PF-1509A and using that I worked out the wiring. So here it is if you have come across this blog and are doing something similar here is the wiring!
Battery - Red/Blue
Rear Speaker Left+ - White/Red
Rear Speaker Left- - Red/Black
Rear Speaker Right+ - Blue/Yellow
Rear Speaker Right- - Red/White
GND - Black
Switched Power - Yellow/Green
Front Speaker Left+ - Brown/White
Front Speaker Left- - Green
Front Speaker Right+ - Red/Yellow
Front Speaker Right- - Black/White
iLL+ (external device) - White/Yellow [didn't need this and isn't connected to anything]
iLL- (external device) - Yellow/Green [didn't need this and isn't connected to anything]
So the finished stereo is now wired in and working great!